The present invention relates to naturally aspirated, internal combustion engines; and more particularly to anti-icing heaters for carburetors of such engines.
In near freezing atmospheric temperatures, the carburetor of an internal combustion engine is very vulnerable to the formation of ice in the throat of the carburetor, on the choke and throttle plates, and over the gasoline venturi orifices. This condition is referred to as "classic icing." In addition, if water is left standing around the choke or throttle plates, it may freeze when the engine is unused for a prolonged period of time in freezing atmospheric temperatures. In this case, the choke and throttle plates become stuck in a closed or near closed position and the engine will not start. The degree of classic icing in a carburetor throat during operation of the engine is dependent upon the amount of water vapor or the water content in the air. The freezing of water around the throttle plates, for example due to the engine's sitting unused overnight, is more susceptible to other sources of water, such as from the engine crank case vent tube required for emission control.
Several phenomena control the amount of ice build-up within the carburetor. The first phenomenon is decompression of intake air produced by the engine cylinder vacuum. Such decompression causes the intake air temperature to drop which may cause the air to go below the freezing point depending upon the ambient temperature intake, the amount of pressure reduction, and the flow rate of the air. The amount of pressure drop the air experiences can be controlled by the carburetor throat design and the throttle plate position.
An air intake temperature below freezing often causes the water vapor to condense and then freeze on a surface of the carburetion system which is also less than zero degrees Celsius. Another factor effecting ice build-up is residual water left in the carburetor throat from the previous operation. Such water can freeze the choke plate, throttle plate and cover the gasoline diffusion venturi nozzle.
A common solution to this problem in the use of the manually operated damper is a manifold heat exchanger that collects hot air off the exhaust manifold or the exhaust pipe of the engine. The collected hot air is directed by duct work into the carburetor. This mechanism has a winter and summer setting to prevent overheating of the gasoline in the carburetor during warm weather operation. The drawback of such a system is that the damper must be controlled manually depending upon the season of operation.